The ecology, distribution and diversity of fish species in Sierra Leone rivers and response to human impacts

Abstract

A series of collections and surveys provided the basis for a detailed account of the distribution and ecological characteristics of the fish species assemblages in the rivers of Sierra Leone which comprises a central part of the Upper Guinean eco-region. Within and between river differences were analysed and a high degree of statistical similarity was found between the species composition of the major rivers. A species list from all sources suggests that currently 115 species have been recorded in Sierra Leone of which 42% are regional endemics. Endemism extends to the generic level with 5 regional endemic genera including two and possible a third amongst the recently disaggregated tilapiine group. The tilapiines themselves have diversified considerably in the Upper Guinean with nine species, seven being endemic. The drivers of this considerable diversification generally in the Upper Guinean are discussed.

Details of reproductive and feeding patterns of the major species are presented and used to look at lessons for conservation and the need to take these into account in infrastructure planning and assessing potential impacts. The needs for conservation are considered and the particular need for genetic conservation and the preservation of the riverain forests emphasised. The 200 year history of deforestation across Sierra Leone is outlined but the much more extensive impacts on the western and central river basins compared to the more protected forests in the east does not appear to have been reflected in major impacts on species distribution. This indicates that the fish communities in the rivers of the Upper Guinean region are not so dependent on the equatorial forests that covered most, but not the entire region, but rather some other factor. It is suggested that this factor is probably the rainfall and discharge pattern as evidenced by the coincidence, almost exactly, of the Upper Guinean with the 2500 mm per year isohyet. Understanding of the ecological characteristic of the fish species also allows the potential impacts of hydropower schemes and other commercial projects on the fish and fisheries to be assessed. Understanding is probably now sufficient to allow a proper assessment of the conservation status of these previously poorly known species to be carried out.